The present invention relates to a magnetic disk drive that can operate in a low-pressure environment, and more particularly to a technology for controlling a magnetic disk drive whose information storage area increases when the environment becomes favorable.
The following patent documents are referred to below by ordinal number, and are hereby incorporated by reference:                1. Japanese Patent Laid-open No. 9-245419; and        2. Japanese Patent Laid-open No. 2002-298532.        
Magnetic disk drives are now used in all product fields due to the development of advanced electronic devices. For example, magnetic disk drives are now mounted in external storage devices and home personal computers and other electronic devices. These devices are used indoors. Therefore, magnetic disk drives for indoor use can be designed on the presumption that they remain stationary.
However, the operating environment surrounding magnetic disk drives is not always favorable for the magnetic disk drives. Magnetic disk drives used in notebook computers, car navigation systems, and other mobile applications are subject to keyboard input impact, vibration caused during vehicle motion, and various other severe operating conditions which must be taken into consideration.
In addition to the severe operating conditions associated with mobility, the physical environment surrounding a magnetic disk drive is not always favorable for magnetic disk drive operation. If, for example, a magnetic disk drive is mounted in a small airplane or other vehicle, the ambient pressure varies greatly. Further, users are now demanding magnetic disk drives that can operate at altitudes of more than 3000 m above sea level.
Magnetic disk drives are usually designed so that a control operation does not start to inhibit data recording when a slider, on which a magnetic head is mounted, decreases its flying height unless an atmospheric pressure decrease and a temperature increase both occur. In a high-temperature, low-pressure environment, however, the slider fails to fly steadily because it comes into contact with the magnetic disk medium that faces it.
Patent Document 1 discloses a magnetic disk drive that can continue to write data in a high temperature environment that exceeds a specified temperature range. Patent Document 2 discloses a magnetic head slider which can maintain a uniform flying height margin in varying low pressure environments.
In a magnetic disk drive that uses a rotary actuator, an actuator arm supporting a slider moves back and forth along an arcuate path over a rotating magnetic disk medium. As a result, a certain angle (yaw angle) is formed between the slider and the direction of magnetic disk medium rotation. Therefore, when the slider moves from the magnetic disk medium's inner tracks to outer ones via intermediate ones or vice versa, the slider's flying height increases at a radial position corresponding to a yaw angle of zero and decreases at the other radial positions. Typically, the slider's flying height increases at the magnetic disk medium's intermediate tracks and decreases at the inner and outer tracks.
In a low-pressure environment, the slider's flying height decreases so that the slider can potentially come into contact with the magnetic disk medium. In a high-temperature environment, the slider's flying height also decreases leading to the same possible contact with the magnetic disk medium. In a magnetic disk drive that uses a rotary actuator, the above-mentioned contact occurs at a specific radial position of the magnetic disk medium and the area affected by such potential contact cannot be used for information storage.